The present invention relates to a process for the production of novel polymeric phosphonic acids based on acrylonitrile polymers and their use as flame retardants in synthetic resins and intumescent coating compositions, e.g., paints.
The manufacture of halogen-free flame retardant combinations is conventional. These use phosphates and polyphosphates (U.S. Pat. No. 3,936,416; DOS 2,839,710=British Pat. No. 2,006,223=U.S. Pat. No. 4,198,493) or phosphonic acids (DOS 2,827,867=European Pat. No. 6,568), optionally in blends with nitrogen compounds and hydroxy compounds. When exposed to flame, these intumescent flame retardants form a fire resistant coke foam on the polymer, thereby shielding the remainder of the material from further effects of fire and heat and contributing toward extinction of the polymer fire. Many flame retardant coating compositions are based on the same fire resistance principle (DOS No. 1,794,343=Canadian Pat. No. 822,594=British Pat. No. 1,074,243, DOS 2,315,416=U.S. Pat. No. 4,013,599).
All of these compositions have the disadvantage that they are unstable with respect to the effects of water and are extracted by water (J. Fire Retard. Chem. 4:154, No. 3 [1977]).